[PATCH 07/32] acpi-video-detect: Rewrite backlight interface selection logic

[Hans de Goede]

Hi,

On 11-06-15 14:28, Jani Nikula wrote:
> On Thu, 11 Jun 2015, Hans de Goede <hdegoede at redhat.com> wrote:
>> Hi,
>>
>> On 11-06-15 11:19, Pali Rohár wrote:
>>> On Wednesday 10 June 2015 15:01:07 Hans de Goede wrote:
>>>> Currently we have 2 kernel commandline options + dmi-quirks in 3 places all
>>>> interacting (in interesting ways) to select which which backlight interface
>>>> to use. On the commandline we've acpi_backlight=[video|vendor] and
>>>> video.use_native_backlight=[0|1]. DMI quirks we have in
>>>> acpi/video-detect.c, acpi/video.c and drivers/platform/x86/*.c .
>>>>
>>>> This commit is the first step to cleaning this up, replacing the 2 cmdline
>>>> options with just acpi_video.backlight=[video|vendor|native|none], and
>>>> adding a new API to video_detect.c to reflect this.
>>>>
>>>> Follow up commits will also move other related code, like unregistering the
>>>> acpi_video backlight interface if it was registered before other drivers
>>>> which take priority over it are loaded, to video_detect.c where this
>>>> logic really belongs.
>>>>
>>>> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
>>>
>>> Hello,
>>>
>>> lot of people are using acpi_backlight parameter in kernel cmdline to
>>> fix some of problems. I would like to see this parameter still working
>>> and to not break existing configuration. E.g acpi_backlight=vendor to
>>> use dell-laptop.ko or thinkpad_acpi.ko backlight.
>>
>> I would have like to keep acpi_backlight= for that exact same reason,
>> but that is not possible while keeping acpi_video as a module.
>>
>> Thinking more about this, this is not strictly true, we could make
>> some other (core) part of the acpi code use __setup to get the
>> acpi_backlight= value and have that part export the value for use
>> in the acpi_video module. This is not really pretty, but I think it
>> may be the best way to solve this.
>
> It just might be a good idea to try to not change the backlight related
> parameters all the time... See [1]. I probably forgot a few.

Right, so as said I'm fine with adding the above work-around to the
next version of the patch-set to keep acpi_backlight=[vendor|video]
working as before.

Regards,

Hans